Why OSPF is electing the wrong DR and BDR?

[GabrielART]

Folks, 

After configuring four routers with loopback0 192.168.0.6 - 192.168.0.9 respectively, Router 9 (loopback0 interface as 192.168.0.9 - highest loopback0 IP) is not becoming the DR. The priorities were not set, and was left as default 1. Also, copied the running configuration and reloaded each router to force a new election process, but they still are not electing R9 as DR and R8 as BDR. Any ideas? Also, refer to the topology picture below and the "show ip ospf interface" on each router to verify that priority were not set, and loopback interface IP were as mentioned before. NOTE: This lab was taken from Neil Anderson's CCNA Training at Flackbox.com. Thanks

[paul driver · Accepted solution]

Hello
on the rtrs
ospf isnt preemptive try :

clear ip ospf process 
test again 

[GabrielART]

That did it Paul. Thanks again for the solution. 

[MHM Cisco World]

If all routers use defualt priority then there is no guarantee which one will be elect as DR/BDR it depends on which one is UP first' i.e. if two routers is UP and already elect DR/BDR when new rputer is add and have prefer priority/router-id then there is no new election process.

For DR/BDR and router ID 

Check below from cisco doc.

https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13685-13.html#toc-hId--438911689

Exstart

Once the DR and BDR are elected, the actual process of the exchange link state information can start between the routers and their DR and BDR.

In this state, the routers and their DR and BDR establish a primary-secondary relationship and choose the initial sequence number for adjacency formation. The router with the higher router ID becomes the primary and starts the exchange, and as such, is the only router that can increment the sequence number. You would logically conclude that the DR/BDR with the highest router ID is the primary for this process. The DR/BDR election could be because of a higher priority configured on the router instead of highest router ID. Thus, it is possible that a DR plays a secondary role. Also, that primary/secondary election is on a per-neighbor basis.

MHM

[GabrielART]

Thank MHM Cisco World for the clarification. It makes sense, since there is no preemption on the election process, OSPF will make the first configured router as the DR, and second as BDR despite their lower loopback numbers. I was surprised that even after saving the running-config and reloading all the routers around the same time, it did not resulted in the right election per loopback interface number. The routers exchange information so quickly, that the first one to come online, will start swapping LSAs with the other online routers, and eventually become the DR. However, clearing the OSPF processes on the router that is not supposed to be the DR, did the trick. 

[MHM Cisco World]

totally correct

MHM